Process for treating nonferrous metals and alloys



Patented Sept. 5, 1933 PATENT OFFICE PROCESS FOR TREATING NONFERROUS METALS AND ALLOYS Ralph F. Cohn, Dixon, Ill.

No Drawing. Application April 16, 1931 Serial N0. 530,725

10 Claims.

This invention leads to a process for the treatment of non-ferrous metals and alloys with an alkali-metal or an alkaline-earth metal.

In many instances it is advantageous to treat non-ferrous alloys, such as lead containing various metallic impurities, with an alkali-metal or an alkaline-earth metal. is in the carrying out of the process described by Guillaume J. Kroll, in U. S. Letters Patent No.

1,428,041, issued September 5, 1922. A further instance is in the production of alloys of lead and the alkali or alkaline-earth metals.

It is common knowledge, however, that when lead containing certain metallic impurities is' treated at molten temperatures with these alkaliforming metals (by which I mean, alkali-metals, rare earth metals, and alkaline-earth metals) the reaction often proceeds at such a rapid rate as to produce a violent explosion. The violence of this reaction prevents the efficient use of alkali forming metals in the refining of certain types of lead by the Kroll process and necessitates the use of alloys of the alkali-forming metal instead. The use of these alloys is disadvantageous in that it requires the introduction into the lead of large quantities of alloying metal, in order to introduce relatively small quantities of the alkaliforming metal. Furthermore, the violence of the reaction makes it impractical to form alloys between certain types of lead and the alkali-forming metal by introducing the latter directly into the lead. For this reason, it has been necessary to resort to indirect methods for producing the alloys, such, for instance, as the electrolysis of salts of the alkali-forming metal in contact with molten lead.

I will discuss the process as applied particularly to metallic calcium'as the alkali-forming metal, since calcium is a reagent commonly employed, but it will be understood that the process is equally applicable to the use of any alkalimetal, alkaline-earth metal, or rare earth metal, which I have called, as a group, alkali-forming metals. It has'long been known that when metallic calcium is added to certain types of impure lead in the molten state, a very violent reaction occurs. The reason for this phenomena has not been known prior to my investigations. I have found that this is not due to any intrinsic property of lead itself but is brought about by the presence of certain metals present therein as impurities. It now appears that this violent reaction occurs only when the lead contains greater than a certain proportion of arsenic, antimony,

One of such instances Some of the metallic impurities of this group may magnesium, zinc, and certain other elements, though with the latter to a lesser extent. These metallic impurities have one property in common. that is, they have high exothermic heats of reaction when uniting to form compounds with calcium. This has led me to believe that the explosion resulting when metallic calcium is added to lead containing more than a certain minimum of any one or combination of these metallic impurities is caused by the local heating resulting from the reaction between the calcium and the metallic impurities whereby the calcium is heated to a temperature sufficient to bring about spontaneous reaction between the calcium and the lead. It is also possible that the action of these metallic impurities is catalytic.

I have found that after these metallic impurities are-removed, or reduced to a certain relatively low percentage, metallic calcium may be introduced in molten lead without danger of ex 75 plosion. Such metals must be reduced to a concentration in which their heat of reaction will not be suflicient to raise the remainder of the calcium to a temperature where spontaneous reaction of the reagent with lead takes place. For example, when only antimony is present its concentration must be below about .08% while magnesium must be below about 0.3 On the other hand, zinc may be as high as about 0.5% without causing a violent explosion.

These impurities may be removed in a number of diiferent ways. For example, an alloy of calcium in amount just sufficient for their removal may be added to the molten lead and the im purities removed in the form of a dross whercupon metallic calcium may be introduced into the molten lead without danger ofexplosion. One suitable alloy of this character is an alloy of calcium and lead which may be added without danger of explosion, but which, in many instances, involves prohibitive expense if utilized to replace all of the metallic calcium used in the process. In some instances it may be advisable to employ metallic magnesium for the removal of other impurities from the lead such as arsenic, antimony, etc. but care should be taken that the amount of magnesium remaining. in the metal under treatment is not sufficient to itself bring about the explosive reaction.

also be removed by blowing the molten impure lead with air, steam, chlorine, or other oxidizing agentsafter which metallic calcium may be introduced either for the purpose of removing impurities not belonging to this highly exothermic group or for the purpose of producing a calcium-lead alloy.

It will be seen that because of my improved process it is no longer necessary to employ calcium-lead alloys for the removal of all of the impurities in the refining of impure lead. The metallic impurities contained in impure lead and belonging in this highly exothermic group are normally relatively small in their total percentage so that if calcium lead alloys are to be employed as a reagent for their removal, only relatively small quantities will be required. The removal of the metals constituting the major proportion of the impurities may be accomplished through the use ol metallic calcium, introduced as such. On the other hand. if some other alternative method is employed for the removal of the impurities of the aforesaid group, calciumlead alloys need not be employed as a reagent.

A distinction should be drawn between me tallic alkali-formii'ig metal as a reagent and alloys of these metals. and where I have used the term a reagent other than an alkali-forming metal or words of similar import, it will be understood that allows of alkali-forming metals, such as calcium-lead alloy, are intended to be included as one of such other reagents.

My improved process also permits the manufacture of calcium-lead alloys directly through the introduction of metallic calcium into the molten lead, one or other of the above mentioned methods being first employed for the removal of metallic impurities of the highly exothermic group.

While I have thus described a specific embodiment of my invention I am aware that numerous alterations and changes may be made therein without materially departing from the spirit of the invention and the scope of the appended claims in which- I claim:

1. The process of treating impure lead with an alkali-forming metal which includes, treating with a lead alloy of an alkali-iorining metal. for reducing to a predetermined maximum in the metal the metallic impurities reacting violently with the alkali-formingmetal. and then introducing the alkali-forming metal into the molten lead.

2. The process of treating impure lead with metallic calcium which includes, treating the impure lead with a calcium--lead alloy for segregating the metallic impurities reacting violently with the alkali-forming metal to leave a concentration in the lead below which explosion does not occur, removing said impurities from the lead, and introducing said alkali-forming metal into the molten lead.

3. The process of treating impure lead with al kali-forming metals which includes, treating the lead with a reagent other than an alkali-forming metal to reduce the antimony content thereof to a predetermined maximum below which it does not bring about violent reaction of the alkaliforming metal and then introducing the alkaliforming metals into the molten lead.

4. The process of treating impure lead with alkali-forming metals which includes, treating the lead with a reagent other than an alkaliforming metal to reduce the arsenic content thereof to a predetermined maximum below which it does not bring about violent reaction of the alkali-forming metal and then introducing the alkali-forming metals into the molten lead.

5. The process of treating impure lead with alkali-forming metals which includes, treating the lead with a reagent other than an alkaliforming metal to reduce the magnesium content thereof to a predetermined maximum below which it does not bring about violent reaction of the alkali-forming metal and then introducing the alkali-forming metals into the molten lead.

6. The process of. treating impure lead with an alkali-forming metal which includes, introducing into the lead a reagent other than an alkaliiorming metal for reducing the metallic impurities reacting violently with the alkali-forming metal to a predetermined maximum below which explosive reaction is avoided, and then introducing the alkali-forming metal into the molten lead.

7. The process of treating impure lead with calcium which includes, treating the lead with means other than an alkali-forming metal for reducing the metallic impurities reacting violently with calcium to a predetermined maximum below which explosive reaction is avoided, and then introducing metallic calcium into the molten lead.

8. The process of treating impure lead with alkali-forming metals which includes, first. reducing the impurities included in the group, arsenic, antimony, magneisum, and Zinc, by means of oxidizing agents, to a predetermined maximum below which explosive reaction of the alkaliforming metal does not occur. and then introducing the alkali-forming metals into the molten lead.

9. The process of treating impure lead with alkali-forming metals which includes, first, reducing the impurities included in the group, arsenic, antimony, magnesium, and Zinc, to a pre determined maximum by means of at least one reagent other than an alkali-forming metal, and then introducing the alkali-forming metals into the molten lead.

10. The process of treating impure lead with calcium which includes, first. reducing the impurities included in the group arsenic. antimony, magnesium. and zinc. to a predetermined maximum below which explosive reaction of the alkaliforming metal does not occur by means of a reagent other than an alkali-forming metal, an then introducing metallic calcium into the molten lead.

RALPH F. COHN. 

